Flashcards in Visual Field 1 Deck (29)
what are the absolute limits for the human eye?
fixation to temporal limit?
temporal: 100 degrees
what is the definition of perimetry
the study of the visual field using targets of various sizes, luminances, colors, and someitmes movements
what is kinetic perimetry
when is it visible?
what kind of things are easier to see?
a stimulus is chosen (of a given size and luminance, or size and color) and is moved from an area where it is not seen to an area where it is seen
-usually moving things are easier to see
what is static perimetry?
when is it first detected?
a location is chosen and the luminance or shape of the stimulus is changed until it is seen
-first detected at threshold
what is an isopter?
a "line" connecting all points of equal visual sensitivites, equal thresholds, and it divides the seeing area from the non-seeing area for a given stimulus
what is the infrathreshold? what is the suprathreshold?
infra: stimulus that are dimmer or smaller than one's threshold
supra: stimulus that are brighter or bigger than one's threshold
what is the hill of vision
what does the base represent
what does the tip represent
the 3D representation using the horizontal axis as the location in visual space and the altitude (vertical direction) as the visual sensitivity at that location.
-base rep absolute boundaries
-tip rep most sensitive region which is the fovea
when horizontal cuts on the hill are made what do we obtain?
when vertical cuts are made what do we obtain?
horiz cuts on the hill are made we obtain an isopter for a given stimulus
vert cuts made we obtain a graph to relate sensitivity from fixation
what is a scotoma
where is it relative to the isopter?
an area of reduced or absent visual sensitivity which is inside the isopter and is surrounded by an area which does not have reduced sensitivity
where is the location of a physiological blind spot? what is the size?
location: its center is located 15.5 degrees temporal to fixation and 1.5 degrees below the horizontal meridian
size: 5.5 degreees wide by 7.5 degrees high
where is the blindspot for the right eye
where is the blindspot of the left eye
located on the right side of the visual field
-bc optic nerve is nasal so it is in the temporal visual field
what does a central scotoma involve?
what does a centrocecal scotoma involve?
the area from the physiological blindspot up to and including fixation
where is the paracentral scotoma?
any scotomoa within 20 degrees from fixation but excluding fixation itself.
-some books say 30 degrees from fixation
where is the arcuate scotoma?
extends from the blind pot and bows over fixation
-arches from the blindspot into the nasal field and follows the course of the retinal nerve fibers
what does a cuneate scotoma involve and where does it extend to
involves the blindspot and extends into the temporal field
what is a depression
an inward turning of an isopter
-it differs from a scotoma in that it is not surrounded by an area visible to the stimulus, it is at an edge
what is a nasal step
nasal step breaks right at the raphe, with a difference in sensitivity on each side of the horizontal divide.
what is a temporal wedge
comes up from the blind spot and extends over temporally
what is an absolute depression called
how are scotomas and depressions related
scotoma can get larger and break through and become a depression
-a scotoma in one isopter can press down on another isopter and cause this isopter to have a depression
what does steep and sloping mean
steeps means its been there and probably isn't progressing
-sloping means changing or developing
what does an amsler grid subtend a 10 degree field? 7 degree feidl?
-a 10 degree field when held approx. 11.3 inches (28.7cm) from the eye
-a 7 degree field when held 16 in from eye
when do we use a tangent screen?
-pts who are unable to sit behind a bowl secondary to a physical condition
-pts w/ markedly reduced central vision who cannot hold fixation in a bowl
-pts who respond better in an open space
in hysterical fields how much is vf constricted
-what is the most common
10 degrees bilaterally
-tubular field: remarkably constant in size, shape, and steepness of margins
what is a tubular field
the field is the same linear size regardless of the distance of the test object from the pts eye
-this also assumes that the visual stimuli subtends the same visual angle at the various testing distances used
what are the advantages to goldmann perimetry
1. both kinetic and static targets may be used
2. both central and peripheral fields may be tested
3. both the target luminance and size may be changed
4. a specific area of the field may be quickly isolated and tested
what are the disadvantages of goldmann perimetry
1. testing the full field is time consuming and tedious
2. bc the exposure time, speed of movement, and point location are not set by the machine, there is some amount of variability among perimetrists